A flock is brought in each year to keep the grass down on the historic site. But a recent local decline in sheep farming has prevented the National Trust from borrowing any.
The hill is too steep to mow safely and a wet May made the grass grow quickly – covering the 180ft chalk outline of the ancient fertility symbol. Rodney Legg, of the Open Spaces Society, said: “The giant has gone from being a white icon, to a green man and into the invisible man.
“Visitors have been disappointed as they can’t really see it. We need more sheep.”
It is unclear when the giant was etched into the hill near Dorchester, Dorset. The first mention of him was in 1694.
In 1868 land owner Lord Rivers ordered “His Mightiness” be restored after it became overgrown. In World War II it was covered to stop German pilots using it for navigation.
The National Trust said it will be rechalked in September.